1. Field of the Invention
The present invention relates to isolated polypeptides having alpha-glucosidase activity and isolated polynucleotides encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods for producing and using the polypeptides.
2. Description of the Related Art
Several enzymes are involved in the degradation of starch. The enzymes include alpha-amylase, beta-amylase, amyloglucosidase, pullulanase, isoamylase, alpha-glucosidase, and cylcodextrin glycosyltransferase.
Alpha-glucosidases (EC 3.2.1.20) hydrolyze terminal, non-reducing alpha-1,4-linked glucose residues in various substrates, releasing glucose. They degrade disaccharides and oligosaccharides quickly while polysaccharides are attacked slowly if at all. Maltose, maltose derivatives, sucrose, aryl-alpha-glucosides, and alkyl-alpha-glucosides can act as substrates.
Other filamentous fungi have been reported to produce alpha-glucosidases such as Aspergillus fumigatus (Rudick and Elbein, 1974, Archives of Biochemistry and Biophysics 1611: 281-290), Aspergillus flavus (Olutiola, 1981, Mycologia 73: 1130), Aspergillus nidulans (Kato et al., 2002, Appl. Environ. Microbiol. 68: 1250-1256), Aspergillus niger (Rudick et al., 1979, Archives of Biochemistry and Biophysics 193: 509), Aspergillus oryzae (Leibowitz and Mechlinski, 1926, Hoppe-Seylers Zeitschrift für Physiologische Chemie 154: 64), Mortierella alliacea (Tanaka et al., 2002, Biosci. Biotechnol. Biochem. 66: 2415-2423), Mucor javanicus (Yamasaki et al., 1978, Berichte des Ohara Instituts für Landwirtschaftliche Biologie 17: 123), Mucor rouxii (Flores-Carreon and Ruiz-Herrera, 1972, Biochemica et Biophysica Acta 258: 496), Penicillium pupurogenum (Yamasaki et al., 1976, Agricultural and Biological Chemistry 40: 669), and Penicillium oxalicum (Yamasaki et al., 1977, Agricultural and Biological Chemistry 41: 1451).
Alpha-glucosidases can be used in combination with other starch-degrading enzymes, e.g., alpha-amylase, to achieve complete hydrolysis of starch in industrial applications where conversion to fermentable sugars is desirable. Consequently, there is a need in the art for alternative alpha-glucosidases with improved properties such as pH optimum, temperature optimum, and thermostability.
It is an object of the present invention to provide polypeptides having alpha-glucosidase activity and polynucleotides encoding the polypeptides.